Cellulose is the most abundant biologically synthesized polymer on earth. It is composed of monomers of the sugar glucose that are joined into long chains by covalent beta (1,4) glycosidic linkages that are formed between the C1 aldehyde and C4 hydroxyl groups of the glucose molecule. This chemical structure imparts to cellulose its crystalline, fibrous physical structure. Various forms of cellulose are major industrial agricultural products, particularly cotton and wood. Cellulose is the major component of many products such as paper, textiles, cardboard, construction materials, and many other products. Most cellulose is obtained from the familiar multi-cellular photosynthetic terrestrial plants. Cellulose is also produced in the oceans by unicellular plankton or algae using the same type of carbon dioxide fixation found in the photosynthesis of land plants.
Certain bacteria can assemble cellulose via non-photosynthetic pathways, requiring glucose, sugar, glycerol, or other organic substrates for conversion into pure cellulose. One such bacterium is Acetobacter xylinum, now taxonomically classified as Gluconacetobacter xylinus. A single Acetobacter xylinum cell can convert up to 108 glucose molecules per hour into cellulose. The Acetobacter cells produce sub-microscopic cellulose fibrils which gather in an entangled mesh to produce a gelatinous membrane known as a pellicle. The microbial cellulose so formed benefits from the absence of lignin or hemicelluloses, and is completely biodegradable and recyclable. Microbial cellulose also provides high strength, consistent dimensional stability, high tensile strength, light weight and excellent durability. It is also extremely absorbent in the hydrated state.
Another advantage of microbial cellulose is the potential for direct membrane assembly during biosynthesis. The medium can be suspended in a mold or desired shape to directly form useful products. Extremely thin, sub-micron, optically clear membranes can be assembled. Intermediate steps of paper formation from pulp are unnecessary, and textile assembly from yarn is unnecessary. Cellulose orientation during synthesis is possible for dynamic fiber forming capabilities, and uniaxially strengthened membranes. Crystallization can be delayed by the introduction of dyes into the culture medium, and the physical properties of the cellulose such as molecular weight and crystallinity can be controlled. Also, from this cellulose the direct synthesis of cellulose derivatives such as cellulose acetate, carboxymethylcellulose, methyl cellulose and other derivatives is possible. It is also possible to control the cellulose crystalline allomorph (cellulose I or cellulose II). Brown, Jr., et al., U.S. Pat. No. 4,954,439 disclose a cellulose-producing microorganism which is capable, during fermentation in an aqueous nutrient medium containing assimilable sources of carbon, nitrogen and inorganic substances, of reversal of direction of the cellulose ribbon extrusion such that a cellulose ribbon-bundle having a width of at least two cellulose ribbons is produced.
Microbial cellulose is not intrinsically electrically conductive. Various efforts have been made to impart electrical conductivity to such cellulose, including thermal transformation, deposition of metallic or other conductive particles, and infusion of dyes Yoshino et al. in Synthetic Metals 41-43, 1593-1596 (1991) describe the pyrolyzation of bacterial cellulose at temperatures from 1000 to 3000° C. to transform it to a graphite material. Evans, et al, Pub. No. U.S. 2003/0113610 discloses a method for the deposition of metals onto bacterial cellulose, where the bacterial cellulose matrix is placed in a solution of a metal salt such that the metal salt is reduced to the metallic form precipitates in or on the cellulose matrix.